The invention pertains generally to injector valves and is more particularly directed to injector valves having increased fuel flow rates.
Fuel injectors of the electromagnetic solenoid type have been commonly utilized in "multipoint" electronic fuel injection (EFI) systems in the automotive field. Such injectors are located at each cylinder of the engine and spray an atomized charge of fuel into the intake manifold near the associated intake valve. As the intake valve opens, the atomized fuel and air from the intake manifold are drawn into the cylinder and are combusted. By controlling the duration of the operational times of the injectors with a pulse width modulated control signal from an electronic pulse width computer, the precision of fuel delivery has been greatly improved for the internal combustion engine. The fuel is metered accurately with respect to the many and varied operating parameters of the engine including MAP, RPM, temperature and others. With this precision is the ability to improve fuel economy, control emissions, or increase driveability such that the conventional carburetor will probably be displaced in the future by the EFI system as the most prevelant fuel control device.
Another recent development in the fuel control field that may hasten the demise of the conventional carburetor is the "single point" EFI system which, like its counterpart the "multipoint" EFI system, depends upon the precision of electronically controlling an electromagnetic solenoid injector.
"Single point" systems usually have one injector for the delivery of fuel to a plurality of cylinders of an engine at a single injection point instead of the "multipoint" system where a one-to-one correspondence occurs. These injection points may be variably placed inside the intake manifold or the throttle bores of an air flow regulation device leading to the intake manifold. If placed in the throttle bores, these injectors may be located above or below the throttle blades for the most advantageous configuration depending on the particular injector structure. With the substitution of one injector for a plurality of injectors, the "single point" EFI system reduces complexity and expense compared to many "multipoint" schemes while retaining most of the attendant EFI system advantages vis a vis the conventional carburetor.
It is desirable to inject such "single point" systems at least once per engine event (revolution) or even as fast at each intake valve opening. Since one injector replaces a plurality of injectors, sometimes as many as four for an eight-cylinder engine with a two-plane manifold, the "single point" injector generally must have a higher fuel flow rate than a corresponding "multipoint" injector. For use in higher displacement engines a higher flow rate electromagnetic solenoid injector would additionally be highly desirable whether "multipoint" or "single point".
This higher flow rate, because of the preferred single point injection timing, must be accomplished without the sacrifice of injector speed. If possible, it would be desirable for increased control that the injector speed should even be increased. If a higher flow rate is obtained at the expense of operating speed, such as injector will not be as advantageous as if both goals are achieved. The slower the injector opening time, the less overall fuel capacity the injector will be capable of delivering in the high speed range of the engine.
Presently in the art an increased flow rate for an injection valve can be obtained by increasing the metering orifice cross-sectional area, increasing the input pressure, or a combination of both. An increase in the input fuel pressure to a single point system would, however, require the additional expense of a higher pressure fuel pump and pressure regulator combination and is, therefore, unacceptable to the basic premise of single point systems, the reduction of complexity.
However, increasing the metering orifice cross-sectional area by scaling up a conventional "multipoint" injector to a "single point" flow rate creates other problems. Initially, the opening time and thus operation capability of the injector is detrimentally affected because of the increase in the mass of the needle valve. The mass of the needle valve increases in proportion to the volume increase of the material and not linearly with the increase in flow rate. Also, the flow paths of conventional "multipoint" valves are unfavorably restricted for "single point" applications and do not have sufficient flow area therethrough to efficiently handle the increased flow rate to a larger metering orifice.
Such "multipoint" valves are illustrated in U.S. Pat. Nos. 4,007,800 issued to Hans, et al., and 3,967,597 issued to Schlagmuller, et al. Hans, et al. and Schlagmuller, et al. disclose the use of a needle valve in an electromagnetic injector having flats cut on four sides of the shaft. This configuration unduly restricts flow through the injector valve and increases needle mass when utilized in a high flow injector.
A U.S. Pat. No. 3,069,099 issued to Graham illustrates a fuel injection nozzle with a three-sided spring retainer plate. Although this configuration does not restrict fuel flow in the pressure operated injection nozzle shown, it is not advantageously suitable for precision electromagnetic solenoid injection valves where exact metering and sure closure are required.
Another problem encountered in scaling up a conventional "multipoint" injector to a "single point" flow rate is that many injectors will not produce a stable flow at different pressures and times. At one particular pressure, for example, the static flow rate will be different some of the time and the instability unpredictable as to occurence. This defect seems to worsen at higher flow rates and higher pressures, and is unacceptable in the "single point" flow rate and pressure range. Changes of between 5%-7% have been noted in the same injector operated at a particular pressure. The unpredictability of a flow rate from an injector will destroy the precision that the EFI systems have brought to the fuel metering art.
This unstable flow problem seems to be centered in the valve seat metering orifice interface where the cylindrical metering orifice truncates the cone of the valve seat. At higher flow rates it is believed that the fuel accelerates through the closure surface and valve seat interface and then, at unpredictable intervals, will not smoothly flow into the exit orifice. If separation occurs at the exit orifice, the fuel will not be precisely metered by the area between the outer wall of the orifice and a pintle of the valve tip. This effect is similar to the "vena contracta" phenomenon found in hydraulics where a fluid under pressure flows around a sharp corner and has an extreme change of momentum and therefore separates from the surface of an orifice.
With high flow injector valves the angle at which the valve seat intersects the cylindrical metering orifice is relatively large because of the shallow cone angle of the valve seat necessary to produce high flow rates with minimal lift from the needle valve. Reducing this intersection angle without modifying the minimal lift conical valve seat would be highly desirable. A modification to the valve seat and valve tip interface of an injector is illustrated at FIG. 4 of a U.S. Pat. No. 3,241,768 issued to Croft, but is for the purpose of developing a constant flow area.
Another problem that prior art injection valves with high flow rates incur is a residual fuel drop being retained on the injector or injector tip surface which effects the precision of fuel injection on subsequent openings. The residual fuel left on the injector will also cause contamination if it evaporates and can obstruct the metering orifice.
Spray pattern shaping has been attempted with "multipoint" fuel injectors and with "single point" injectors. The shaping of the pattern is important in the "single point" applications, since one injector is entraining the fuel in the air flow at a particular time and the consequent change is to be delivered to particular multiples of the cylinders. If the air fuel ratio precision is to be maintained and cylinder-to-cylinder distribution errors minimized, the flow pattern must be correctly designed and reproducible with every injection. This will minimize wall wetting and unwanted condensation of the fuel on the throttle and other surfaces.
One of the spray patterns becoming popular in "single point" injection is the hollow-cone pattern where the fuel is limited to a volume between two differently-sized cones having their apex at the injector tip. It would be advantageous to be able to reproduce such a pattern with the same injector structure over a wide range of operating pressures and flow rates.